The physics of strong-field laser interactions with solids is largely unexplored but is known to involve the nonperturbative sub-cycle motion of electrons and the radiation of high harmonics. Control of these extreme, nonlinear, coupled light-matter interactions for the generation of short wavelength coherent radiation has been problematic. The understanding of the strong-field response in solids is in its early stages, which is markedly different than in dilute gases.
For efficient XUV generation minimizing loss and maximizing the interaction length between the MIR and XUV have been challenging. Further, for attosecond pulse generation including XUV frequency combs, control of the spectral phase of the harmonics to mitigate linear and nonlinear dispersive phase characteristics of the pump propagation is needed.
XUV radiation is highly desirable for investigating and modifying nanoscale structures and ultrafast processes in microelectronics, marking, materials science, and surface physics and chemistry. Its advantages include sub-micron wavelength to provide high spatial resolution, strong absorption to provide surface sensitivity, wavelength-dependent absorption to provide elemental specificity, and attosecond oscillation period to enable the formation of attosecond pulses of coherent radiation. No known source combines all these advantages. However, currently available sources of XUV radiation must employ cumbersome vacuum chambers that contain windowless gas-phase regions or bulky electron accelerators. The vacuum chambers are needed because the existing sources are large and/or incompatible with the matter under investigation, and because XUV radiation cannot travel far in solids or in air. This limits the applications.
What is needed is a solid state device that utilizes non-perturbative light-matter interactions in solids through the combined nanophotonic and strong-field control of light, to provide a compact efficient high repetition rate tunable source of broad-band coherent XUV radiation for spectroscopy, attosecond science, XUV frequency combs, and similar applications.